Silver-free AMB aluminum nitride ceramic copper-clad substrate and preparation method thereof

Abstract

The invention relates to a silver-free AMB aluminum nitride ceramic copper-clad substrate and a preparation method thereof, and the preparation method comprises the following steps: coating a first surface of a ceramic base layer with a solder layer through silk-screen printing, and placing the ceramic base layer coated with the solder layer in an oven for first drying and heating; the ceramic base layer is turned over, the second face of the ceramic base layer is coated with the brazing material layer through silk-screen printing, and then the ceramic base layer coated with the brazing material layer is placed in the drying oven to be dried and heated for the second time; copper metal layers are attached to the two faces of the ceramic base layer with the solder layers respectively to form mother boards, multiple sets of mother boards are arranged according to the measuring range of a vacuum sintering furnace compression column, and all the mother boards are stacked from bottom to top to form a mother board assembly; and putting the mother board assembly into a vacuum sintering furnace for single sintering. By arranging the silver-free solder layer, the brazing performance of the copper-clad substrate is improved, the voidage is reduced from 5%-15% to 1%-5%, and the percent of pass is increased from 80%-90% to 95%.

Description

Technical Field

[0001] This invention relates to the field of ceramic copper-clad substrates, and more particularly to a silver-free AMB aluminum nitride ceramic copper-clad substrate and its preparation method. Background Technology

[0002] Due to their high heat dissipation properties, ceramic substrates are widely used in emerging strategic fields such as rail transportation, aerospace, new energy vehicles, wind power generation, and defense industries. Currently, there are two main types of metallization methods for ceramic substrates: for multi-layer ceramic substrates, there are Low Temperature Co-fired Ceramic (LTCC) and High Temperature Co-fired Ceramic (HTCC) processes; for planar ceramic substrates, there are Direct Bonding Copper (DBC), Thick Film Copper (TFC), Direct Plating Copper (DPC), and Active Metal Brazing (AMB) methods.

[0003] Among them, the AMB process has significant advantages, mainly reflected in the high bonding strength and excellent thermal shock resistance of the products. Compared with the DBC process, the AlN (aluminum nitride) substrate prepared by the AMB process can achieve a peel strength of 10 N / mm and withstand more than 800 thermal shocks.

[0004] However, current methods for soldering ceramic copper-clad substrates all use silver-containing solder, which has the following problems: Traditional AMB substrates often use Ag-Cu-Ti solder with a high silver content (such as 60% silver content). Silver is a precious metal with a high cost, which will significantly increase the substrate manufacturing cost.

[0005] Under conditions of high humidity, high temperature, or electric field, silver atoms may migrate from the solder, forming conductive paths that can lead to short circuits or insulation failure, resulting in a low yield of copper-clad laminates.

[0006] Copper-clad laminates brazed with silver solder are unstable under high-temperature brazing conditions, which can easily lead to interface voids, weak bonding strength, and high defect rate. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a silver-free AMB aluminum nitride ceramic copper-clad substrate and its preparation method, so as to solve one or more problems in the prior art.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A silver-free AMB aluminum nitride ceramic copper-clad substrate, the ceramic copper-clad substrate comprising a ceramic substrate and a copper metal layer, and the following layer located between the ceramic substrate and the copper metal layer: A solder layer containing Cu, Ti and Sn.

[0009] Furthermore, the solder layer is located between the copper metal layer and the ceramic substrate.

[0010] Furthermore, the thickness of the solder layer is 0.01mm to 0.1mm.

[0011] Furthermore, the weight percentages of Cu, Ti, and Sn in the solder layer are: Sn 10%–20%, Ti 1%–15%, and the remainder Cu.

[0012] Accordingly, the present invention also provides a method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate, comprising the following steps: The solder layer is applied to the first surface of the ceramic substrate by screen printing, and the ceramic substrate coated with the solder layer is placed in an oven for the first drying and heating. Remove the ceramic substrate, flip it over, and apply the solder layer to the second side of the ceramic substrate through screen printing. Then place the ceramic substrate coated with the solder layer in an oven for a second drying and heating. A copper metal layer is attached to both sides of a ceramic substrate with a solder layer to form a mother plate. Multiple mother plates are set according to the pressure column range of the vacuum sintering furnace, and the mother plates are stacked from bottom to top to form a mother plate assembly. Apply a pressure of 0-30 MPa to both ends of the motherboard assembly and evacuate to 10 MPa. -3 Pa, the motherboard assembly is placed in a vacuum sintering furnace for single sintering. The single sintering is divided into two stages, including a first stage sintering and a second stage sintering. The first stage sintering temperature is 400-500℃, and the holding time is 30-90 minutes. Then, the motherboard assembly that has undergone the first stage sintering is subjected to a second stage sintering. The second stage sintering temperature is 800-1200℃, and the holding time is 10-160 minutes.

[0013] Furthermore, the solder layer is prepared by mixing Cu, Sn, Ti and an organic binder at a mass ratio of 1:3 to 30.

[0014] Furthermore, the first drying heating temperature or the second drying heating temperature is 80° to 120°, and the first drying heating time or the second drying heating time is 8 min to 20 min.

[0015] Furthermore, an isolation sheet is provided between adjacent mother plates. The isolation sheet is made of high-purity graphite material, and the thickness of the isolation sheet is 0.5mm to 50mm.

[0016] Furthermore, the organic binder is terpineol and ethyl cellulose.

[0017] Furthermore, the solder layer needs to be cleaned and dried on the ceramic substrate before screen printing, and the drying time is 30 min to 80 min.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention uses a silver-free solder layer instead of a silver-containing solder layer, which not only reduces the material burden but also significantly lowers the cost. The price of 1 kg of silver-free solder is between 300 and 1000 yuan, which is more than 10 times lower than the cost of silver-containing solder.

[0019] Furthermore, by setting a silver-free solder layer, the soldering performance of the copper-clad substrate was improved, the void ratio was reduced from 5%–15% to 1%–5%, the pass rate was increased from 80%–90% to 95%, and the silver-free solder, because it does not contain silver, can eliminate the potential failure problem caused by silver ion migration from the source.

[0020] Furthermore, the peel strength of the copper-clad substrate is improved by setting a silver-free solder layer. Compared with the silver-soldered AMB aluminum nitride ceramic copper-clad substrate, the peel strength of the copper-clad substrate prepared by this invention is 10-30 N / mm. The silver-free solder layer can form a more uniform interface reaction layer with better mechanical properties, providing stronger interface bonding and stress state. Attached Figure Description

[0021] Figure 1 The diagram shows a schematic representation of the structure of a silver-free AMB aluminum nitride ceramic copper-clad substrate and its preparation method according to an embodiment of the present invention.

[0022] Figure 2 The image shows a scanned image of the silver-free solder layer during the brazing of a silver-free AMB aluminum nitride ceramic copper-clad substrate and its preparation method according to an embodiment of the present invention.

[0023] Figure 3 The image shows a scanned image of a silver-free AMB aluminum nitride ceramic copper-clad substrate and its preparation method according to an embodiment of the present invention, with a silver solder layer brazing.

[0024] The following labels are used in the attached diagram: 1. Isolation sheet; 2. Solder layer; 3. Copper metal layer; 4. Ceramic base layer. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a silver-free AMB aluminum nitride ceramic copper-clad substrate and its preparation method. The advantages and features of this invention will become clearer from the following description. It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clearly illustrate the purpose of the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0026] Please refer to Figure 1 The silver-free AMB aluminum nitride ceramic copper-clad substrate of this embodiment includes a ceramic substrate 4 and a copper metal layer 3, as well as the following layer located between the ceramic substrate 4 and the copper metal layer 3: The solder layer 2 contains Cu, Ti, and Sn. The weight percentages of Cu, Ti, and Sn in the solder layer are: Sn 10%–20%, Ti 1%–15%, and the remainder Cu. Cu, as the main component, imparts good electrical and thermal conductivity to solder layer 2, ensuring the fundamental electrical performance of the AMB aluminum nitride ceramic copper-clad substrate. Sn in solder layer 2 lowers the melting point and improves wettability. Ti can chemically react with the surface of the ceramic substrate 4 to form strong chemical bonds, effectively enhancing the adhesion between solder layer 2 and the ceramic substrate 4.

[0027] Furthermore, the solder layer is made by mixing Cu, Sn, Ti and an organic binder in a mass ratio of 1:3 to 30, and the organic binder is terpineol and ethyl cellulose.

[0028] For further details, please refer to... Figure 1 The solder layer 2 is located between the copper metal layer 3 and the ceramic substrate 4, and the thickness of the solder layer 2 is 0.01mm to 0.1mm.

[0029] Accordingly, the present invention also provides a method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate, the method comprising the following steps: Before screen printing, the ceramic substrate, which is an aluminum nitride ceramic sheet, needs to be cleaned and dried. The drying time is 30 to 80 minutes. The purpose of cleaning is to remove oil, dust, impurities, and other contaminants from the surface of the aluminum nitride ceramic sheet to prevent contaminants from being mixed into the solder layer. At the same time, it improves the adhesion of the adhesive layer in the solder layer and avoids subsequent delamination.

[0030] Step 1: Using a 100-300 mesh screen printing stencil, the solder layer 2 is applied to the first side of the ceramic substrate 4 through screen printing. The ceramic substrate 4 coated with the solder layer 2 is then placed in an oven for the first drying and heating. The first drying and heating temperature is 80°C to 120°C, and the heating time is 8 min to 20 min.

[0031] Step 2: Take out the ceramic substrate 4 after the first drying, turn the ceramic substrate 4 over and apply the solder layer 2 to the second side of the ceramic substrate 4 through screen printing. Then place the ceramic substrate 4 coated with the solder layer 2 in an oven for a second drying and heating. The second drying and heating temperature is 80° to 120° and the heating time is 8 min to 20 min.

[0032] The purpose of the first and second drying and heating processes is to evaporate the solvent in the adhesive layer, so that the adhesive layer can be initially cured and formed, thus avoiding problems such as adhesive layer flow and pattern deformation in subsequent processes.

[0033] Step 3: Copper metal layers 3 are bonded to both sides of the ceramic substrate 4 with solder layer 2 to form a master plate. Multiple master plates are set according to the pressure column range of the vacuum sintering furnace, and the master plates are stacked from bottom to top to form a master plate assembly. Isolation plates 1 are placed between adjacent master plates. The isolation plates are made of high-purity graphite material with a thickness of 0.5mm to 50mm. The isolation plates 1 prevent solder layer 2 from overflowing, and due to the high-temperature resistance and chemical stability of high-purity graphite, they also provide heat insulation and uniform heat distribution, preventing localized overheating and cracking of the ceramic substrate 4, and ensuring the flatness and consistency of the product.

[0034] The motherboard assembly is placed in a vacuum sintering furnace. A pressure of 0-30 MPa is applied to both ends of the motherboard assembly through the upper and lower pressure heads, and a vacuum is drawn to 10⁻³ Pa. The assembly undergoes a first-stage sintering process in the vacuum sintering furnace at a temperature of 400-500°C for 30-90 minutes to ensure thorough glue removal. The motherboard assembly that has undergone the first-stage sintering process is then subjected to a second sintering process at a temperature of 800-1200°C for 10-160 minutes. Ti, as an active metal, preferentially combines with N atoms in AlN to form TiN. Simultaneously, the freed Al atoms diffuse into the solder alloy. The reaction can be expressed as: 4AlN + 3Ti = 3TiN + 4Al. The generated TiN forms a continuous and dense reaction transition layer at the interface between the AlN ceramic and the solder, effectively improving the wettability of the ceramic and the metal solder and enhancing the interfacial bonding strength. Cu and Sn in the solder mainly fill the gaps and form a metal connection layer. After sintering and cooling, the above-mentioned motherboard assembly (bng) is obtained to obtain a ceramic copper-clad substrate.

[0035] Please refer to Figure 2 and Figure 3 The cooled ceramic copper-clad substrate is subjected to ultrasonic scanning or X-ray scanning to obtain images ( Figure 2 It can be observed that, compared to Figure 3 The scan image of the silver solder layer shows slight voids (i.e., the white areas in the image), while... Figure 2 The silver-free solder layer shows fewer voids and no white areas in the soldering scan, which greatly reduces solder voids. The silver-free solder improves the soldering performance of AMB aluminum nitride ceramic copper-clad substrates, reducing the void rate from 5%–15% to 1%–5% and increasing the pass rate from 80%–90% to 95%. Moreover, the silver-free solder, because it does not contain silver, can eliminate the potential failure problem caused by silver ion migration at the source.

[0036] Since the main body of solder layer 2 is copper, its strength, hardness and elastic modulus are much higher than those of silver. On the other hand, the diffusion rate of Ti in Cu is different from that of silver. When cooling at the high temperature of brazing, due to the different shrinkage of metal and ceramic, huge thermal residual stress will be generated at the interface.

[0037] The following is a comparison of the performance of different embodiments with and without a silver solder layer: Table 1: Composition List of Silver Solder Layer

[0038] Table 2: Composition List of Silver-Free Solder Layer

[0039] Table 3: Performance Comparison of Silver Solder Layer and Silver-Free Solder Layer under Different Brazing Conditions:

[0040] As can be seen from the above, when both silver-solder AMB aluminum nitride ceramic copper-clad substrates and silver-solder AMB aluminum nitride ceramic copper-clad substrates are subjected to a test temperature of -45℃ to 150℃, with each cycle of high and low temperature constant temperature for 0.5h, a conversion time of 15s, and 300 cycles, the number of newly added voids inside the silver-solder AMB aluminum nitride ceramic copper-clad substrate is 0.7%, while the number of newly added voids inside the silver-solder AMB aluminum nitride ceramic copper-clad substrate is 1.0%.

[0041] For silver-soldered AMB aluminum nitride ceramic copper-clad substrates, the peel strength between the ceramic substrate and the copper metal layer is 15-40 N / mm. For silver-free AMB aluminum nitride ceramic copper-clad substrates, the peel strength is 10-30 N / mm. Table 3 shows that using a silver-free solder layer further improves the peel strength, significantly reduces the void ratio after high-temperature cycling, and greatly reduces solder costs.

[0042] Based on the above test results, it can be concluded that the bonding strength of the silver-free solder AMB aluminum nitride ceramic copper-clad substrate described in this invention is at the same level as that of the silver-containing AMB aluminum nitride ceramic copper-clad substrate, and can meet the reliability requirements.

[0043] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0044] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silver-free AMB aluminum nitride ceramic copper clad substrate, characterized by, The ceramic copper clad substrate comprises a ceramic base layer and a copper metal layer, and a layer between the ceramic base layer and the copper metal layer, wherein the layer comprises: a solder layer containing Cu, Ti and Sn.

2. The silver-free AMB aluminum nitride ceramic copper clad substrate according to claim 1, wherein, The solder layer is between the copper metal layer and the ceramic base layer.

3. The silver-free AMB aluminum nitride ceramic copper clad substrate according to claim 1, wherein, The thickness of the solder layer is 0.01mm-0.1mm.

4. The silver-free AMB aluminum nitride ceramic copper clad substrate according to claim 1, wherein, The component weight percentage of Cu, Ti and Sn in the solder layer is: Sn 10%-20%, Ti 1%-15%, and the rest is Cu.

5. The method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate as described in any one of claims 1 to 3, characterized in that... The method comprises the following steps: applying the solder layer to the first surface of the ceramic base layer by screen printing, and placing the ceramic base layer with the solder layer in an oven for the first time for drying and heating; taking out the ceramic base layer, turning over the ceramic base layer, applying the solder layer to the second surface of the ceramic base layer by screen printing, and placing the ceramic base layer with the solder layer in an oven for the second time for drying and heating; attaching the copper metal layer to the two surfaces of the ceramic base layer with the solder layer to form a mother board, setting multiple groups of mother boards according to the pressure column range of the vacuum sintering furnace, and stacking the mother boards from bottom to top to form a mother board assembly; The mother plate assembly is subjected to a pressure of 0-30 MPa at both ends and vacuumized to 10 Pa -3 Pa, and is subjected to single sintering in a vacuum sintering furnace, the single sintering being divided into two stages, including first stage sintering and second stage sintering, the first stage sintering being at a temperature of 400-500°C for 30-90 min; and the mother plate assembly subjected to the first stage sintering is subjected to the second stage sintering, the second stage sintering being at a temperature of 800-1200°C for 10-160 min.

6. The method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate as described in claim 5, characterized in that: the solder layer is made by mixing Cu, Sn, Ti and an organic binder in a mass ratio of 1:3-30.

7. The method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate as described in claim 5, characterized in that: The first drying and heating temperature or the second drying and heating temperature is 80-120°, and the first drying and heating time or the second drying and heating time is 8-20min.

8. The method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate as described in claim 5, characterized in that: An isolation sheet is arranged between adjacent mother boards, the isolation sheet is made of high-purity graphite material, and the thickness of the isolation sheet is 0.5-50mm.

9. The method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate as described in claim 6, characterized in that: The organic binder is terpineol and ethyl cellulose.

10. The method for preparing a silver-free AMB aluminum nitride ceramic copper-clad substrate as described in claim 5, characterized in that: The ceramic base layer needs to be cleaned and dried before screen printing of the solder layer, and the drying time is 30-80min.

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